Hitherto, a turbofan including a plurality of blades formed into a three-dimensional shape has been widely employed as a blower fan to be installed in a ceiling-concealed air conditioner. For example, the following turbofan is disclosed in Patent Literature 1. In each of the blades, a concave-shaped portion is formed at substantially a center part in an axial direction (height direction) in a leading edge section, and convex-shaped portions are formed at parts on a main plate side and on a shroud side in the leading edge section. In each of the blades, the leading edge on the shroud side is positioned on the forward side in the rotational direction with respect to the leading edge on the main plate side.
In the turbofan configured as described above, the leading edge section is inclined forward so that, as described above, the shroud side of the leading edge section of the blade is positioned on the forward side in the rotational direction with respect to the main plate side of the leading edge section. Therefore, the fan can appropriately adapt to the velocity distribution of the suction flow, and the flow is less liable to separate on the shroud side.
Further, with the concave-shaped portion formed at the center position in the height direction and the convex-shaped portions formed respectively on the shroud side and on the main plate side, even when the airflow rate is lower than the design point, a large-scale separation vortex, which is generated at the blade leading edge section, may be decreased in size. Specifically, the separation vortex is divided into two small vortices by the two convex-shaped portions, to thereby decrease the size of the separation vortex and suppress reduction in area just behind the blade entrance, which is caused when the vortex is formed so as to block the entrance. As a result, reduction in noise and increase in efficiency can be expected not only at the design point but also when the airflow rate is low.
Further, for example, in Patent Literature 2, there is disclosed a turbofan including a plurality of blades each having a stepped surface formed at the leading edge so as to be formed into a discontinuous shape in the span direction. The stepped surface is formed as an inclined surface having a predetermined inclination angle with respect to a plane perpendicular to the rotational axis. Further, there is also disclosed a mode configured so that, in the leading edge of each of the blades, a part closer to the hub with respect to the stepped surface is formed into a shape that is gradually protruded forward from the stepped surface toward the hub, in other words, the chord length of each of the blades is changed so as to increase from the stepped surface toward the hub.
In the turbofan configured as described above, the flow turbulence is caused through collision with the discontinuous surface, and thus a longitudinal vortex is formed. Then, this longitudinal vortex suppresses the separation of the flow along the blade surface, and thus the noise during air blowing can be reduced.
Further, for example, in Patent Literature 3, there is disclosed a turbofan in which a ridge direction of the blade is substantially parallel to the axial direction, and a plurality of corner portions are formed in the leading edge of the blade. The leading edge of the blade is formed into such a stepped shape that the leading edge is positioned forward in the rotational direction toward the hub side.
In the turbofan configured as described above, the flow turbulence is caused through collision with the corner portions, to thereby generate two longitudinal vortices. The vortices suppress the separation. Thus, the air blowing noise can be reduced, and the air blowing efficiency can be improved.